Development and validation of a standardized oxidation assay for the accurate measurement of the ability of different wines to form “de novo” oxidation-related aldehydes

Abstract

From the standpoint of wine aroma oxidation there are two effects observed: aroma degradation of oxygen sensitive compounds (polyfunctional mercaptans) and the appearance of new substances with high aromatic power (acetaldehyde, methional, phenylacetaldehyde, sotolon, alkenals, isobutanal and 2, 3-metylbutanals) (1-5). According to our experience, Strecker aldehydes are compounds with highest sensory relevance in the oxidative degradation of many wines (5-7). Based on previous research, it was observed that these compounds can be already present in freshly bottled wines, free from any sign of oxidation; forming stable, non-volatile and odorless complexes with sulfur dioxide (8). During storage in the bottle these compounds are released as the level of free SO2 decreases by oxidation causing a shift in the SO2-aldehyde adduct chemical equilibria. Moreover, wine aldehydes can be formed throught direct oxidation of their precursors (“de novo” formation), when the free SO2 level is under 5 mg/l (7-8). The main goal of this work is to study the intrinsic ability of the wines for the formation of “aldehydes de novo”. Hence, a method to consume oxygen at controlled doses, at 45 ° C, has been developed. This oxidation method allows to reach de novo formation of aldehydes on a fast way (2-7 days) depending on the wine. The validation of this method is carried out maintaining the same oxidation conditions at 25º C. In addition, the same wines have been submitted to consecutive air saturation cycles (9) for means of comparation. The proposed strategy comprises the study of eight red wines in duplicate, each wine underwent three increasing oxygen doses. The analysis carried out at the beginning at the and end of the oxidation were: aminoacids, metals, free and total SO2, total carbonyl compounds, acetaldehyde, color, IPT, Folin, as well as major and trace aroma compounds. The results show that this is a reproducible method of oxidation, which allows to reach de novo formation of aldehydes at all doses studied. Different profiles of oxygen consumption are obtained depending on the age and previous contact with oxygen, temperature had a strong effect on the formation of Strecker aldehydes with respect to the oxygen consumed.

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